The present invention is directed to an improved drum vent filter. More particularly, the present invention is directed to an improved vent filter which has improved hydrogen gas permeability.
Disposing of toxic waste, especially transuranic waste, presents modern societies with a daunting challenge. The waste is produced at one site, such as an industrial site or power generation site and must be eventually transported to a waste disposal or a waste storage site. Transporting these materials is hazardous because the materials are transported by trucks over existing highway systems. Frequently these materials generate gases which are also hazardous. The gases may result in combustion which can disperse the waste before the waste reaches the waste disposal or waste storage site. It has been determined that hydrogen gas is generated by radioactive waste. Accordingly, the Department of Transportation has set limits on the amount of hydrogen gas in a container of radioactive waste which may be safely shipped even if the container is vented. The rate of venting is therefore an important consideration because it is desirable to vent as much gas from the container as possible before the container is shipped and while the container is awaiting permanent storage. After the drum has been filled with waste such as transuranic waste, it is important that the gas being vented is filtered so as to remove particulate matter which may be radioactive and also to impede the diffusion of volatile organic compounds (VOCs) out of the drums.
In view of these considerations, there is a need to improve the drum vent filters currently used.
In view of the aforementioned considerations, the present invention is directed to an improved drum vent filter for filtering hydrogen gas to remove particles therefrom. The drum vent filter comprises an annular housing having an axially extending portion with a threaded exterior surface and a cylindrical interior surface defining a cylindrical interior space with first and second axial openings. The cylindrical interior surface has an annular lip therein having an axially facing support surface and a free surface. The free surface is spaced a selected distance from the first axial opening and the support surface is spaced a selected difference from the second axial opening. A radial flange extends outwardly from the outwardly extending portion of the housing and has a top surface which is flush with the second opening of the cylindrical interior surface and a bottom surface adjacent the threaded exterior surface of the cylindrical portion. A cylindrical filter element comprised of a carbon-to-carbon filter media is disposed within the cylindrical space and has a bottom surface abutting the annular lip and a top surface flush with the top surface of the radial flange. The filter element is retained within the cylindrical space with a peripheral layer of adhesive sealant. Disposed in spaced relation to the top surface of the radial flange is a lid which defines an axial gap between the top surfaces of the filter element and radial flange and a radial gap between the top surface of the radial flange and the bottom surface of the lid. An annular seal is disposed about the cylindrical portion of the housing and abuts the bottom surface of the radial flange wherein the axial gap between the bottom surface of the lid has a height in the range of about 0.125 inch to about 0.175 inch, and preferably about 0.150 inch; wherein the cylindrical space has a diameter of at least 0.8 inch and wherein the housing has an axial length no greater than about 0.375 inch, whereby diffusion of hydrogen gas through the vent is enhanced.
In a further aspect of the invention, the carbon-to-carbon filter media has a thickness in the range of one quarter to three-tenths inch, a density of 0.2 to 0.3 g/cm3 and a diameter in the range of 0.60 inch to 1 inch and preferably about 0.70 inch.
In a further aspect of the invention, the housing has overall height in the range of 0.65 inch to 0.85 inch, and preferably about 0.75 inch and is made of type 304 stainless steel.